1. Field of Invention
The present invention relates to current interrupter operations used in cathodic protection of metallic structures such as pipe lines, and more particularly to truly independent remote monitoring methods, systems and apparatus for validating the operation of such interrupters.
2. Description of the Prior Art
In a typical setting, buried steel structures such as pipelines for oil and gas have permanent cathodic protection provided by connecting the output of a DC voltage source to the structure (pipeline) and to ground. Tests of the state of cathodic protection must be made regularly, preferably at least once a year, to determine the effectiveness of the cathodic protection along the structure. In order to perform such tests, a current interrupter device is introduced. This device cyclically interrupts the cathodic protection provided by the voltage source that protects, for example, a stretch of a pipeline structure. The cycled interruption is generally scheduled to occur during the day so that testing may be performed. At night, the cathodic protection is ordinarily left “on” by programming the current interrupter accordingly. Any suitable interruption cycle may be employed, for example, the current may be left “on” in cycles that are 3 times longer than the “off” cycles, and these cycle times may run, for example, from one to ten seconds. The interruption cycles during the day allow a crew of test operators to walk along the buried structure (pipeline) with specialized data gathering equipment to perform required tests. Once a current interrupter is installed, it will ordinarily remain in place for several days adjacent to the voltage source (such as a rectifier) while test operators make measurements along the pipeline far away from the source.
Constant monitoring of the current interrupter operations is important, because a malfunction of a current interrupter may invalidate any testing performed during the malfunction. Without monitoring the current interrupter, test operators working away from the source may later discover that the system was not working properly, potentially wasting and invalidating several hours or even days of testing activity, and leaving the structures unprotected during that time.
One system that monitors the operation of a current interrupter is disclosed in U.S. Pat. No. 6,625,570. However, this patent discloses complicated complete replacement systems that not only control the voltage source, but also require prior knowledge of the cycle times. Such systems are impractical and expensive, requiring a user having an existing cathodic protection system to buy a whole new system.
There are several types of DC (direct current) power sources used in cathodic protection systems, the majority of which are rectifiers for use with AC (alternating current) power line power. Others include solar panels having DC outputs where a rectifier may control the amount of DC voltage and current that is output to the structure. Another example is a thermal electric DC used, for example, where a natural gas pipeline has no access to solar or the AC power grid. In these cases, a natural gas company may use some of the gas to heat/run a thermal electric generator. This derived DC voltage and current for cathodic protection may be controlled by a rectifier and must be tested, interrupted as described above. Other examples of cathodic protection systems that may be interrupted and tested include sacrificial anodes, and bonds between pipelines. In the cathodic protection regulations, all current sources that may be influencing the structure to soil measurement must be interrupted to insure proper on and off cathodic protection voltage readings.
It is therefore desirable to provide monitoring methods, systems and apparatus for use in cathodic protection systems to verify the operation of current interrupters used during periodic testing that may be temporarily installed or used with a wide variety of current interrupter systems regardless of the sequence or cycle times used by the systems, thereby providing a truly independent verification of the testing of the cathodic protection system, or verification of the operation of the cathodic protection system itself.